U.S. Pat. No. 4,503,717 issued Mar. 12, 1985 on "Shock Actuated Unit" shows an actuator in which a controlled member is urged in a predetermined direction by a spring or other yielding means, and is releasably retained against movement in that direction by a latching mechanism. The latching mechanism is released automatically when subjected to a shock force of predetermined magnitude, to free the member for spring induced movement which may for example effect closure of a controlled valve. The controlled member is also manually actuable by a hand wheel or other manual operating element, to actuate the valve by hand between its different positions and to vary the position at which the latching mechanism retains the member. The apparatus of that prior Patent includes a differential gear arrangement for adjusting the relationship between the manually operated control element and the other portions of the apparatus.